1 / 29

Energy-Efficient Process Cooling

Energy-Efficient Process Cooling. Process Cooling Systems . Cooling systems Cooling tower Water-cooled chiller Air-cooled chiller Absorption chiller Compressed air cooling Cooling costs assume: Electricity: $0.10 /kWh Natural gas: $10 /mmBtu Water: $6 /thousand gallons.

harsha
Télécharger la présentation

Energy-Efficient Process Cooling

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Energy-Efficient Process Cooling

  2. Process Cooling Systems • Cooling systems • Cooling tower • Water-cooled chiller • Air-cooled chiller • Absorption chiller • Compressed air cooling • Cooling costs assume: • Electricity: $0.10 /kWh • Natural gas: $10 /mmBtu • Water: $6 /thousand gallons

  3. Cooling Tower • 500-ton tower delivers 7.5 mmBtu/hr • Ppump = 18 kW Pfan = 20 kW Water = 120 gal/mmBtu • Unit cost of cooling = $1.22 /mmBtu

  4. Chillers

  5. Water-Cooled Chiller • E/Q = 0.8 kW/ton = 67 kWh/mmBtu • Unit cost of cooling = $6.70 /mmBtu

  6. Air-Cooled Chiller • E/Q = 1.0 kW/ton = 83 kWh/mmBtu • Unit cost of cooling = $8.30 /mmBtu

  7. Absorption Chiller • E/Q = 1 Btu-heat / Btu-cooling Eff-boiler = 80% • Unit cost of cooling = $12.50 /mmBtu

  8. Open-Loop Water Cooling • DT = 10 F V = 12,000 gallons / 1 mmBtu • Unit cost of cooling = $72 /mmBtu

  9. Compressed Air Cooling • 150 scfm at 100 psig to produce 10,200 Btu/hr cooling • 4.5 scfm per hp • Unit cost of cooling = $272 /mmBtu

  10. Relative Process Cooling Costs Near order of magnitude difference in costs!

  11. Cooling Energy Saving Opportunities • Reducing end use cooling loads and temperatures • Add insulation • Add heat exchangers • Improve heat transfer • Improving efficiency of distribution system • Reducing friction using large smooth pipes • Avoiding mixing • Employing variable-speed pumping • Improving efficiency of primary cooling units • Use cooling tower when possible • Use water-cooled rather than air-cooled chiller • Use variable speed chillers

  12. End Use: Add Insulation • Insulation: • Reduces heat transfer into cooled tanks & piping • Decreases exterior condensation • Even at small temperature differences insulating cold surfaces is generally cost effective

  13. End Use: Continuous Process with Sequential Heating and Cooling Current: Qh1 = 100 Qc1 = 100 With HX: If Qhx = 30, Qh2 = 70 Qc2 = 30 HX reduces both heating and cooling loads!

  14. End Use: Batch Processes with Discrete Heating and Cooling Cost effective to transfer heat between processes, whenever the processes that need cooling are 10 F higher than the process that need heating

  15. End Use: Batch Processes with Discrete Heating and Cooling Add Heat Exchangers T = 145 F Requires Cooling T = 120 F Requires Heating

  16. End Use: Optimize Heat Exchanger Network (Pinch Analysis) For multiple heating and cooling opportunities, optimize heat exchanger network using Pinch Analysis.

  17. End Use: Improve Heat Transfer Cross flow cooling of extruded plastic with 50 F chilled water from chiller

  18. End Use: Improve Heat Transfer Counter flow Cross flow Parallel flow e = 0.78 e = 0.62 e = 0.50 NTU = 3 and Cmin/Cmax = 1

  19. Cooling Product: Cross vs Counter Flow Cross Flow: e = 0.69 • Tw1 = 50 F • Tp = 300 F • Mcpmin = 83.2 Btu/min-F • Q = e mcpmin (Tp – Tw1) = 0.69 83.2 (300 – 50) • Q = 14,352 Btu/min Counter Flow: e = 0.78 • Q = 14,352 Btu/min • Tp = 300 F • Mcpmin = 83.2 Btu/min-F • Q = e mcpmin (Tp – Tw1) = 14,352 Btu/min = 0.78 83.2 (300 – Tw1) • Tw1 = 79 F

  20. Cooling Product: Cross vs Counter Flow Cooling towers can deliver 79 F water much of the year using 1/10 as much energy as chillers!

  21. Distribution System: Avoid Mixing Separate hot and cold water tanks Lower temperature, less pumping energy to process Higher temperature, less fan energy to cooling tower

  22. Primary Cooling: Match Cooling Source to End Use

  23. Primary Cooling: Use Cooling Tower When Possible Cooling towers can deliver water at about outside air temperature

  24. Primary Cooling: Use Cooling Tower When Possible CoolSim reports number hours CT delivers target temperature. Model cooling tower performance

  25. Primary Cooling: Use Water Cooled Chillers for Year Round Loads E/Q (Air-cooled) = 1.0 kW/ton E/Q (Water-cooled) = 0.8 kW/ton

  26. Primary Cooling:Stage Multiple Constant Speed Chillers

  27. Primary Cooling: Use Variable-Speed Chiller

  28. Ammonia Refrigeration Systems Multiple compressors, stages, evaporative condensers

  29. Ammonia Refrigeration Savings Opportunities • Reclaim heat • Variable head-pressure control

More Related